SS-31, also known as elamipretide or MTP-131, is a synthetic tetrapeptide that has attracted significant research attention for its targeted effects on the inner mitochondrial membrane. Unlike many research peptides, SS-31 has been studied in human clinical trials. This overview specifically addresses ss-31 peptide research, and related research is indexed on PubMed.
Structure and Mitochondrial Targeting
SS-31 is a tetrapeptide: D-Arg-Dmt-Lys-Phe-NH2. Alternating aromatic and basic residues give it a positive charge that drives accumulation in the inner mitochondrial membrane (IMM), which maintains approximately −180 mV electrochemical potential. Once there, SS-31 interacts with cardiolipin — a phospholipid essential for organizing electron transport chain complexes.
Why Cardiolipin Matters
Cardiolipin stabilizes ETC complexes I, III, and IV and is essential for cytochrome c function. Cardiolipin oxidation — caused by excess ROS — disrupts ETC organization, reduces ATP synthesis, and promotes apoptosis. SS-31 binds cardiolipin and is reported to prevent its peroxidation, protecting ETC function.
Human Clinical Trial Data
Barth Syndrome: A Phase II trial (TAZPOWER) examined elamipretide in Barth syndrome — a rare genetic cardiolipin metabolism disorder. The trial reported improvements in exercise tolerance and muscle weakness. Heart Failure (HFpEF): A Phase II trial (EMBRACE-HFpEF) examined elamipretide in heart failure patients. The primary endpoint was not met, but secondary analyses showed improvements in some cardiac functional measures.
Major Update: Elamipretide Is Now FDA-Approved for Barth Syndrome
This is a significant and relatively recent development worth stating clearly: on September 19, 2025, the FDA granted accelerated approval to elamipretide HCl (brand name Forzinity, Stealth BioTherapeutics) for the treatment of Barth syndrome in adult and pediatric patients weighing at least 30 kg — making it the first approved therapy for this ultra-rare mitochondrial disease and the first SS-peptide-class compound to reach full drug approval for any indication. The approval was based on the TAZPOWER trial data referenced above, specifically improvements in knee extensor muscle strength, which the FDA considered “reasonably likely to predict” meaningful functional benefits such as improved ability to stand or walk. Administration is once-daily by subcutaneous injection.
Two important caveats accompany this approval. First, it is an accelerated approval — a regulatory pathway used for serious conditions with unmet need, based on a surrogate or intermediate endpoint (muscle strength) rather than a hard clinical outcome, and continued approval may depend on verification of clinical benefit in a confirmatory trial. Second, the approval is specific to Barth syndrome — an ultra-rare genetic disorder of cardiolipin metabolism affecting primarily males, with distinct underlying biology from the general population. This approval does not extend to, or provide safety/efficacy evidence for, elamipretide/SS-31 use in heart failure (where the EMBRACE-HFpEF trial’s primary endpoint was not met, as described above), general aging, or any other off-label context sometimes discussed in research and biohacking communities.
Frequently Asked Questions
Does elamipretide’s Barth syndrome approval mean it’s proven effective for heart failure or general mitochondrial support?
No. The approval is specific to Barth syndrome based on the TAZPOWER trial’s muscle-strength endpoint. The separate EMBRACE-HFpEF heart failure trial did not meet its primary endpoint, and no approval or comparable trial evidence exists for general anti-aging or mitochondrial-support use.
What does “accelerated approval” mean in practice?
It’s a pathway allowing earlier approval for serious diseases with unmet medical need, based on a surrogate endpoint reasonably likely to predict clinical benefit, with continued approval contingent on confirming that benefit in further study — a meaningfully different (and provisional) evidentiary bar than standard full approval.
Is Forzinity the same product as RUO-labeled “SS-31” sold as a research compound?
The active molecule is the same peptide, but Forzinity is an FDA-approved, prescription pharmaceutical product manufactured under cGMP standards specifically for Barth syndrome, while RUO research-market SS-31 has not completed that regulatory pathway and is not intended for human administration — the same distinction discussed throughout this site’s guide to research peptides vs. pharmaceutical compounds.
View the full SS-31 compound profile with complete citation list.
Research reference only. SS-31/elamipretide is investigational except where specifically approved. Not medical advice.
